Field of the Invention
The present invention relates to an optical module having a structure in which an optical device including multiple optical elements is connected to a control device by use of wiring.
Description of the Related Art
There have been growing demands for increases in speed and capacity of optical communication in recent years. To meet the demands, there has been used parallel optical transmission configured to transmit optical signals in parallel by using multiple optical fibers or optical waveguides.
In an optical module used for the parallel optical transmission, an integrated, downsized, and high-density circuit is subject to an increase in mutual inductance between neighboring wires, which leads to crosstalk between signals traveling through the wires. The crosstalk further increases when high-frequency signals are used therein. For this reason, the occurrence of crosstalk is a major problem in an optical element which uses high-frequency signals. Accordingly, there has been a request for reducing crosstalk in order to pursue downsizing and higher densification of such an optical element.
As a method of reducing crosstalk between signals, according to the technique described in Japanese Patent Application Publication No. Hei 5-251820, wiring for connecting a laser array to a printed board involves alternate arrangement of lines connected to p-type electrodes of lasers and lines connected to n-type electrodes of the lasers, in which the lines connected to the n-type electrodes are used as the ground. As a result, the wiring has a structure in which each signal line is sandwiched by ground lines, and crosstalk between the signal lines can thereby be reduced.
Meanwhile, according to the technique described in Japanese Patent Application Publication No. 2002-261372, wiring for connecting an optical device and a driving device involves alternate arrangement of lines connected to anode electrodes of the optical device and lines connected to cathode electrodes of the optical device, in which the lines connected to the cathode electrodes are connected to a reference potential line. As a result, the wiring has a structure in which each signal line is sandwiched by ground lines, and crosstalk between the signal lines can thereby be reduced.
FIG. 7 is a schematic diagram of an optical module used in the parallel optical transmission, and having a configuration in which signal lines and ground lines are alternately disposed as in the case of the techniques described in Japanese Patent Application Publications No. Hei 5-251820 and No. 2002-261372. The optical module includes: an optical device 2 having multiple optical elements 1; a control device 3 configured to control the optical device 2; and a substrate 4 having multiple lines 4a and 4b on its surface. The control device 3 is disposed on the substrate 4 in such a way as to be in contact with the multiple lines 4a and 4b. Each of the lines 4a and 4b is connected to one end of a wire 5 and the other end of the wire 5 is connected to a corresponding one of an anode terminal 6a and a cathode terminal 6b annexed to each of the multiple optical elements 1. The wires connecting the lines 4a to the anode terminals 6a and the wires connecting the lines 4b to the cathode terminals 6b are alternately disposed along the surface of the substrate 4. According to this configuration, the multiple optical elements 1 and the control device 3 transmit and receive signals therebetween through the lines 4a and 4b, the wires 5, and the terminals 6a and 6b. 
In this optical module, each line 4b connected to the corresponding cathode electrode 6b is connected to the ground on the control device 3 side. Accordingly, the optical module has a structure in which each signal line is sandwiched by ground lines.
The configuration in which the signal lines and the ground lines are alternately disposed, as in the case of the techniques described in Japanese Patent Application Publications No. Hei 5-251820 and No. 2002-261372, may exhibit an insufficient crosstalk reduction effect along with further advances in the downsizing and the high densification. For this reason, there is a demand for another technique that can further reduce the crosstalk.